Triple Boot Help Please

Hey, I'm typically a noob at linux at the moment.
So, I'm on MacOSX 10.5.5. And I'm using VMware Fusion to boot Ubuntu 8.04. I'm trying to boot Linux via this guide. Triple Boot via BootCamp - OnMac.net Wiki
But thing is, I already have my windows partioned and I have no idea what to do to partion my existing MacHDD so it will be partioned.